/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Builds a URL for game spawned by the editor (not including map name!).
The URL for the game
virtual [FString](API\Runtime\Core\Containers\FString) BuildPlayWorldURL ( const TCHAR * MapName, bool bSpectatorMode, [FString](API\Runtime\Core\Containers\FString) AdditionalURLOptions )